Some of you may have been following our coverage of the Samsung 840 EVO slow down issue. We first reported on this issue last September, and Samsung issued a fix a couple of months later. This tool was effective in bringing EVOs back up to speed, but some started reporting their drives were still slowing down. Since our January follow up, we have been coordinating with Samsung on a possible fix. We actually sent one of our samples off to them for analysis, and have just received this statement:

In October, Samsung released a tool to address a slowdown in 840 EVO Sequential Read speeds reported by a small number of users after not using their drive for an extended period of time. This tool effectively and immediately returned the drive’s performance to normal levels. We understand that some users are experiencing the slowdown again. While we continue to look into the issue, Samsung will release an updated version of the Samsung SSD Magician software in March that will include a performance restoration tool.

A look at the reduced read speeds of stale data on an 840 EVO which had the original fix applied. Unpatched drives were slowing much further (50-100 MB/s).

So it appears that Samsung is still looking into the issue, but will update their Magician software to periodically refresh stale data until they can work out a more permanent fix that would correct all affected 840 EVOs. We have not heard anything about the other TLC models which have been reported to see this same sort of slow down, but we will keep you posted as this situation develops further.

We first saw the Silicon Motion SM2256 controller at Flash Memory Summit, but now we've seen it live, in action, and driving several different types of TLC NAND.

Silicon Motion had this live demo running on a testbed at their suite:

The performance looked very good considering the 2256 is designed to efficiently push TLC flash, which is slower than MLC. As their representative was explaining that the SM2256 is currently being tested with Samsung, Toshiba, and SK Hynix TLC flash, I noticed the HDTune write trace:

Those familiar with HDTune and Samsung SSDs with Samsung's TurboWrite cache (from the 840/850 EVO) will recognize the above - the SSD begins writing at SLC speed and after that cache is full, the SSD then drops to writing at TLC speed. I specifically asked about this, as we've only Samsung flash provisioned with an SLC portion of each die, and the answer was that Toshiba and SK Hynix TLC flash also supports such a subdivision. This is good news, as it means increased competition from competing SSDs that can accomplish the same SLC burst writes as the Samsung EVO series.

We heard from a few vendors that will soon be launching SM2256 equipped SSDs this year, and we eagerly await the opportunity to see what they are capable of.

Al first introduced us to Low Density Parity Check, the successor to BCH code error correction when he visited Marvell at FMS 2014 and was shown the 88SS1093 controller. Lite-On has used a slightly different chip, the 88SS1074 to provide LDPC to their new CV2 family of solid state drives. In addition to the new error detection capabilities the new controller offers 256-bit AES encryption and device sleep modes to enhance the battery life of mobile devices. The controller has 4 channels and is paired with 128, 256 or 512GB of triple level cell Toshiba A19 NAND which we have seen on Corsair, OCZ and Silicon Motion products. The press release references results of 4KB throughput at 100,000 IOPS which we hope to be able to verify in the future.

Not only does Samsung's new 850 EVO family introduce us to three dimensional triple level cell NAND, it also incorporates an SLC cache to boost write speeds. The Tech Report received the 250GB and 1TB models to test, with a spotlight on how they fared against the 840 Pro and 840 Evo. Their testing shows that the new way of creating NAND has helped mitigate the reduction in speed which accompanied the first generation of TLC drives. There is no question that the SLC write cache also helps as long as it has space available but this new technology does come with a price, expect $500 for the 1TB and $150 for for the 250GB model. The 5 year warranty is a nice touch for those who have reliability concerns.

"Samsung's long-awaited 850 EVO SSD employs three-dimensional NAND with three bits per cell. It augments that TLC storage with an SLC write cache, and it has a higher endurance rating and longer warranty than most MLC drives. We've taken a closer look to see how it holds up against the competition."

If you own a Samsung 840 SSD, it appears that after much repeated and vocal pressure, Samsung has acknowledged the slow down also affects your drive. We're not talking about the EVO or the Pro, this is the original pure TLC model that launched (the EVO is a TLC+SLC cache hybrid while the Pro is all MLC). Here's the quote from Samsung, via Computer Base:

What? You can't read German? Neither can we, but paraphrasing from the poor quality translation from several online tools, we deduce that Samsung has acknowledged the issue on the 840, and is working on a solution as quickly as possible. This is similar verbiage to the statement issued for the 840 EVO acknowledgement.

** Update **

Thanks to Zyhmet, who commented shortly after posting, here's a human translation:

Because of the feedback we got, we realized that, accessing specific data with units of SSD 840 could lead to lower reading performance.

For the moment our experts are systematically examining the SSD-units with different system environments and we are working on a solution as fast as possible.

Due to different technologies the PRO-series (840 PRO and 850 PRO) are not affected.

Samsung

** End update **

Side note - of those who have used the 840 EVO Performance Restoration Tool, a few have reported an issue cropping up. The error manifests as a SMART data misreporting error:

What's odd about this error is that it was present on some of our pre-production test samples (firmware EXT0AB0Q), and was corrected once we updated those samples to the first retail build (EXT0BB0Q). The image above was an actual screen shot taken during our temperature-dependency testing of the slow down issue. While none of our samples had the issue return when updating all the way to the performance restored firmware, one of those updates did corrupt the Master File Table, rendering the majority of the SSD inaccessible. While we have seen no other reports of corrupted partitions, severalusers noticed the SMART reporting issue after updating. It's odd to see this sort of a regression with firmware updates, in that a bug fixed in the initial shipping firmware has returned (for some) in a subsequent update. If you've updated your 840 EVO with their Performance Restoration Tool, it may be a good time to check your SMART attributes. If you see the error above, please leave us a note in the comments.

Circling back to the slow down issue - given that it is present in two TLC-based SSDs from Samsung, one has to wonder if this issue exists in other Samsung TLC SSDs as well. Here's the list of potentials (thanks to an anonymous comment on a prior story):

840 EVO - 19nm TLC

840 - 21nm TLC

PM841 - 21nm TLC

PM851 - 21nm TLC (some SKUs)

845DC EVO - 19nm TLC

PM843 - 21nm TLC

PM853T - 21nm TLC

We have several questions out to Samsung on these issues, but to date they have not been answered. More to follow as we wait for an official (English) response.

Investigating the issue

"We acknowledge the recent issue associated with the Samsung 840 EVO SSDs and are qualifying a firmware update to address the issue. While this issue only affects a small subset of all 840 EVO users, we regret any inconvenience experienced by our customers. A firmware update that resolves the issue will be available on the Samsung SSD website soon. We appreciate our customer’s support and patience as we work diligently to resolve this issue."

Over the past week or two, there have been growing rumblings from owners of Samsung 840 and 840 EVO SSDs. A few reports scattered across internet forums gradually snowballed into lengthy threads as more and more people took a longer look at their own TLC-based Samsung SSD's performance. I've spent the past week following these threads, and the past few days evaluating this issue on the 840 and 840 EVO samples we have here at PC Perspective. This post is meant to inform you of our current 'best guess' as to just what is happening with these drives, and just what you should do about it.

The issue at hand is an apparent slow down in the reading of 'stale' data on TLC-based Samsung SSDs. Allow me to demonstrate:

You might have seen what looks like similar issues before, but after much research and testing, I can say with some confidence that this is a completely different and unique issue. The old X25-M bug was the result of random writes to the drive over time, but the above result is from a drive that only ever saw a single large file write to a clean drive. The above drive was the very same 500GB 840 EVO sample used in our prior review. It did just fine in that review, and at afterwards I needed a quick temporary place to put a HDD image file and just happened to grab that EVO. The file was written to the drive in December of 2013, and if it wasn't already apparent from the above HDTach pass, it was 442GB in size. This brings on some questions:

If random writes (i.e. flash fragmentation) are not causing the slow down, then what is?

How long does it take for this slow down to manifest after a file is written?

Just minutes ago at the Flash Memory Summit, Samsung announced the production of 32-layer TLC VNAND:

This is the key to production of a soon-to-be-released 850 EVO, which should bring the excellent performance of the 850 Pro, with the reduced cost benefit we saw with the previous generation 840 EVO. Here's what the progression to 3D VNAND looks like:

3D TLC VNAND will look identical to the right most image in the above slide, but the difference will be that the charge stored has more variability. Given that Samsung's VNAND tech has more volume to store electrons when compared to competing 2D planar flash technology, it's a safe bet that this new TLC will come with higher endurance ratings than those other technologies. There is much more information on Samsung's VNAND technology on page 1 of our 850 Pro review. Be sure to check that out if you haven't already!

Another announcement made was more of an initiative, but a very interesting one at that. SSDs are generally dumb when it comes to coordinating with the host - in that there is virtually no coordination. An SSD has no idea which pieces of files were meant to be grouped together, etc (top half of this slide):

Stuff comes into the SSD and it puts it where it can based on its best guess as to how it should optimize those writes. What you'd want to have, ideally, is a more intelligent method of coordination between the host system and the SSD (more like the bottom half of the above slide). Samsung has been dabbling in the possibilities here and has seen some demonstrable gains to be made. In a system where they made the host software aware of the SSD flash space, and vice versa, they were able to significantly reduce write latency during high IOPS activity.

The key is that if the host / host software has more control over where and how data is stored on the SSD, the end result is a much more optimized write pattern, which ultimately boosts overall throughput and IOPS. We are still in the experimentation stage on Storage Intelligence, with more to follow as standards are developed and the industry pushes forward.

It might be a while before we see Storage Intelligence go mainstream, but I'm definitely eager to see 3D TLC VNAND hit the market, and now we know it's coming! More to follow in the coming days as we continue our live coverage of the Flash Memory Summit!

Samsung has just announced a new line of SSDs, based on three bit per cell (TLC) memory, for enterprise customers. The Samsung 845DC EVO is rated at 530MB/s reads with 87,000 IOPS. The company will also cover up to 600TB of writes under its warranty (no mention of length in years, though). The drive will be available "later this month" in 240GB, 480GB, and 960GB models. Samsung did not mention price in their press release, but Anandtech claims the 240GB will be $250, the 480GB will be $490, and the 960GB will be $969.

Samsung's SSDs will give you some TLC???

This is basically $1/GB scaling, plus $10. I must admit, this is getting pricy. In the consumer space, we have recently seen 512GB for $199. That said, SSDs are not known for sticking to their MSRP. Also, these are enterprise-rated drives. Being TLC-based, I wonder how much (if any) SLC-style write cache was included, as per the consumer 840 EVO.

Lastly, Samsung claims that these drives use around 4W under load. This is much lower than hard drives but a little high for SSDs, according to benchmarks that I have seen. That said, there are a few ways to parse that (for example, if they mean that its peak is typically 4W, which would be pretty good for a 960GB drive).

The Samsung 845DC EVO will be available later this month for a little over $1/GB.